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  #1  
Old 05-04-2017, 09:42 PM
timmy timmy is offline
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Default 1961 draft tube or pcv

I've been looking at changing the draft tube out with a pcv and running it into the carburetor and wanted to know if anyone else has tried this and if so what size spacer under the carb did you use. The one that was on there before was tapered from 1/2 inch on the front to about 5/32 in in the back. has anyone just swapped it out with a 1 inch all around?
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Old 05-04-2017, 10:57 PM
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Sounds simple, right?
There's a lot more to venting a block than just a PCV. First, you don't want to create a vacuum in your block because that will promote more blowby and your oil consumption will increase (by a lot).

There are a few ways to do this and I suggest you go online to weigh all your options. Some are 'passive' and others are not. Block ventilation is a system that should be completely understood and carefully applied. Each 'change' after the vent tube was mandated by the EPA. Some changes are very beneficial and others, not so much. - Dave
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Old 06-11-2017, 08:39 PM
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Default PCV on '61

I removed the down draft tube and inserted the PCV below the carburetor. Works great. I have a very slight bulge in the hood since the air filter is raised up a bit, but it's only noticable if you look for it. I think I may have posted some pictures here in the forum. If I can find my post, I will post the link here.

Edit: Here's the link:

http://squarebirds.org/vbulletin/showthread.php?t=19573

if this doesn't work, have a look for posts with the title Road draft v. PCV, that's a thread i asked back in 2015, and got lots of great input from the fine folks who support this forum.

~g
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Old 06-12-2017, 12:05 PM
pbf777 pbf777 is offline
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QUOTE: First, you don't want to create a vacuum in your block because that will promote more blowby and your oil consumption will increase (by a lot). - Dave[/quote]

Please expound further on your experience/knowledge on this subject.

Thank you, Scott.
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Old 06-12-2017, 01:53 PM
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Engine sits at a slight angle so you need the tapered spacer to level out the carb on the '60 and keep the floats happy - may be the same on the '61?.

The '60 already has a tapered phenolic spacer and you could add a flat one with PCV on top if there was enough clearance (will have to get longer carb studs).

There is a short tapered phenolic spacer with PCV for the square bore intake - most are listed as 429 Cobra Jet spacers and go for crazy money.

Geoff's link has a lot of good info and some from me too -

Ironic that this popped up - had an annoyance with my PCV that I was planning on posting. Since my car is a '60 but the replacement engine is a '66 block and '64 heads and '65 intake and rather than cloggin up Tim's thread with my problems - I just created my own thread over in the Squarebird forum.

Pop on over - may be something in there that will help too.

Link
http://www.squarebirds.org/vbulletin...ad.php?t=21668

Last edited by DKheld : 06-12-2017 at 02:39 PM.
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Old 06-12-2017, 06:05 PM
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Quote:
Originally Posted by simplyconnected View Post
...First, you don't want to create a vacuum in your block because that will promote more blowby and your oil consumption will increase (by a lot)...
Quote:
Originally Posted by pbf777 View Post
Please expound further on your experience/knowledge on this subject. Thank you, Scott.
If you're asking for specifications, they are all over the net. In a nutshell, negative block pressure ruins oil control on the cylinder walls which promotes engine wear. Also, piston rings rotate. Sometimes the gaps align but this is random.

The prindle in a PC valve is designed to allow a metered volume of gas to be pulled into the intake (and re-burned). If PCV air flow is restricted or blocked in a closed system, your engine will run rich.

A properly vented PCV system eliminates and re-burns a mixture of fresh air and blowby. Otherwise, emissions will show much more oil being burned.

An old, tired engine usually produces much more blowby than a PCV system can handle because the piston rings are sloppy, they don't have the expansion pressure, cylinder walls are smooth and rings hydroplane over the oil.

I hope this helps. - Dave
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Old 06-13-2017, 10:55 AM
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Cool Sorry about picture postings

Quote:
Originally Posted by GeoffInCarlsbad View Post
I removed the down draft tube and inserted the PCV below the carburetor. Works great. I have a very slight bulge in the hood since the air filter is raised up a bit, but it's only noticable if you look for it. I think I may have posted some pictures here in the forum. If I can find my post, I will post the link here.

Edit: Here's the link:

http://squarebirds.org/vbulletin/showthread.php?t=19573

if this doesn't work, have a look for posts with the title Road draft v. PCV, that's a thread i asked back in 2015, and got lots of great input from the fine folks who support this forum.

~g
Sorry about the ads coming up in the pic posts. That was before I learned to properly post pictures to the forum without those irritating ads from photo-bucket. When I get the time, I will re-post those pictures properly.

Lastly, Dave is 100% on target, and I think the key is making use of the PCV Regulator Valve to ensure proper one-way flow. My motor has been running very well, burns no oil, starts on first turn of the key, and has been quite reliable with this system.
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Old 06-13-2017, 11:27 AM
pbf777 pbf777 is offline
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QUOTE=simplyconnected If you're asking for specifications, they are all over the net.

Yes, I realize there is all kind of "information" over the net; but we are here, and I was curious of any good and accurate information on the subject you may provide, not necessarily "specifications" but just a general understanding on the subject.

QUOTE: In a nutshell, negative block pressure ruins oil control on the cylinder walls which promotes engine wear.

I guess, one would need to define "ruins oil control", for a better understanding of what/which function that has been lost. Please?

QUOTE: Also, piston rings rotate. Sometimes the gaps align but this is random.

This is understood; but are you indicating this frequency changes with crankcase pressure (within the applicable values of coarse)?

QUOTE: The prindle in a PC valve is designed to allow a metered volume of gas to be pulled into the intake (and re-burned). If PCV air flow is restricted or blocked in a closed system, your engine will run rich.

In my experience, understanding that the P.C.V. valve is a metered vacuum leak as referenced by the carburetor; if blocked, the required air volume is then acquired thru the carburetor venturis hence fuel enrichment. And I suppose at some point in the process of acquiring a negative pressure value in the crankcase, the air volume/density thru this controlled "leak" would not remain constant (within the original intentions anyway, and with all other fuctions and considerations nominal), and therefore upset the "state-of-tune", O.K..

I am always interested in the knowledge that can be provided by others, but, I find that often I choose to explore beyond that which others wish to participate (probably just hard-headed) so bear with me.

Thank you, Scott.
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Old 06-13-2017, 05:21 PM
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I did not find nor can I take credit for this information. Racers have tried pulling a hard vacuum on their engines and found many interesting facts. The vacuum adds HP to the rotating assembly because:
  • There is no such thing as 'windage' in a vacuum so air resistance is minimized,
  • Piston rings are sucked tighter to the cylinder walls giving a much better seal,
  • Oil on those walls is also sucked down leaving less lubrication,
  • Since more oil is atomized, blowby consists of more oil which is immediately sucked out,
  • Blowby is augmented by the vacuum, especially when the piston ring gaps align, causing a 'blow torch' through the oil control slots. Remember, these gasses are still burning when the piston reaches BDC.
The affects also promote premature and accelerated ring wear which is never good in a street engine.

PCV valves are first and foremost a CHECK VALVE in one direction, so a backfire will not send fuel mixture into the crankcase. The valve totally shuts off. In the normal operating direction, flow is metered by the spring tension. This allows a small amount of crankcase fumes and fresh air into the intake for re-burning. Too much flow would constitute a vacuum leak which would cause a lean condition.
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Old 06-14-2017, 01:22 PM
pbf777 pbf777 is offline
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[quote=simplyconnected]There is no such thing as 'windage' in a vacuum so air resistance is minimized,

Yes, but since we really aren't creating a true "vacuum", I think one would address this as only reducing the atmospheric pressure (within the crankcase, some), results in the reduction of air density, thus a reduction in the resistance/mass imparted on the units in motion within. So yes, available power increases (at elevated R.P.M.s), but I think a greater benefit is acquired thru the ring function and sealing effect.

[quote]Piston rings are sucked tighter to the cylinder walls giving a much better seal,

On older engines, the applied pressure of the ring upon the cylinder wall was derived greatly (not solely) from the radial tension (spring) of the ring (first & second in relevant examples) it's self. Later it was established that one could use the differential in the pressure above (cylinder volume) and below (crankcase) to apply pressure behind the ring ("pressure-back" rings) to "seat" against the cylinder wall for sealing effort.
This allowed a reduction in that static mechanical radial tension, therefore in a four stroke application engine, reducing frictional drag losses, as the increased load was applied as needed (varying with the pressure differential) on the compression and ignition strokes with a reduction of load (and wear) otherwise.
Taking this a step further, engine builders (both racers & O.E.M.s) realized that one could increase these benefits, by simply increasing this differential, would allow further reductions in the ring's radial tension and a further reduction in frictional losses hence additional available power and efficiency. This even included intentional routing of cylinder pressure to rings thru "gas-holes" (vertical) or "gas slots" (horizontal) to the backside of the ring (generally upper ring). Look at today's ring package from the O.E.s in standard production, it's "racier" than anything that was available before the 1980s.
So, it's difficult to perceive how a minor reduction (compared to cylinder pressure spikes) in crankcase pressure imparted by the P.C.V., only under the conditions of high manifold vacuum (idle, low load cruise, & deceleration, during relatively low cylinder pressures), would significantly increase blow-by and oil consumption?

[quote]Oil on those walls is also sucked down leaving less lubrication,

Also, if additional oil were to pass the ring pack, (oil consumption) then wouldn't this act as additional lubrication (even excessive) and therefor perhaps a reduction in wear?
Since the crankcase is a closed environment (oil & atmosphere at equal pressures) then where is the force (sucking) applied to the oil on the cylinder walls? If reducing the atmospheric density allows the mechanical components to move with less "windage" drag, then does not the same apply to the oil in motion also within the crankcase which is directed (splashed) to the cylinders?

[quote]Since more oil is atomized, blowby consists of more oil which is immediately sucked out,

Since one has created a P.C.V. system which "drafts" the crankcase, it is important to control the velocity (hence the P.C.V. valve) and baffle the flow, so as to reduce carry-over of excessive oil vapor to the induction system. And perhaps this is one arena where one may perceive oil-burning after a P.C.V. system conversion or system failure. And yes, if your engine does suffer from excessive wear/damage and exhibits excessive blow-by, then it may not be possible to configure a closed crankcase ventilation system (P.C.V.) that will not lead to excessive oil consumption/burning. If the ventilation system can not maintain pace with blow-down rate the pressure will build within the crankcase reducing the pressure differential across the ring stack and defeat it's function.

[quote]Blowby is augmented by the vacuum, especially when the piston ring gaps align, causing a 'blow torch' through the oil control slots. Remember, these gasses are still burning when the piston reaches BDC

Yes, one would anticipate that as the differential increased the rate of flow thru an orifice (ring gaps) would also.
Except in abnormal instances, the flame front propagation is extinguished prior to entering the space below the piston dome between the piston head and cylinder wall, particularly by the ring lands. This is particularly known as a problem with emissions as an area for accumulation of unburnt hydrocarbons, with many attempts to solve.

Please find my responses as exploratory in nature, as with the more information presented, such provides for a more thorough understanding.

Scott.

Last edited by pbf777 : 06-14-2017 at 07:31 PM.
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